To an increasing extent in motor vehicles, arrangements to protect the occupant, such as belt tensioners, force limiters used in belt retractors or else gas generators for gas bag modules are adapted in their performance according to the severity of the accident and the position of the occupant. The information of relative and absolute belt webbing withdrawal is very helpful here.
In belt retractors in which the driving spring for winding the belt webbing is assisted by a motor in order to ensure increased comfort in the fastened state, it is necessary in addition to detect the absolute belt webbing position in order to determine whether the belt is in the placement position or is moving at all. Depending on requirements, the assisting motor can then be activated.
It is therefore an object of the invention to provide a belt retractor with a belt webbing withdrawal measurement arrangement and respectively a method to determine the belt webbing withdrawal in a belt retractor, by means of which the belt webbing withdrawal and respectively the belt webbing position can be determined in a simple manner.